Questions that pertain to solid geometry will require you to be familiar with the "volumes" of solid objects, most often simple rectangular shapes and cylindrical shapes. On a few of the harder GRE math questions, you'll need to be familiar with the concept of a diagonal in a rectangular shape. You'll need to be able to distinguish between the surface area and volume

For a rectangular or cylindrical 3D object, you'll need to memorize the formulas for the volume and surface area.

Any tricks that you may encounter will most likely involve having to change between units or will require you to use various properties of triangles.